Sec-ylbiphenyl composition and process for preparing the same

ABSTRACT

A water-white, essentially odorless liquid useful as a dieletric oil and as a dye solvent, particularly for a carbonless paper solvent, consisting essentially of about 82% to about 88% by weight of mono-sec-butylbiphenyl and about 12% to about 18% of di-sec-butylbiphenyl prepared by reacting highly pure 1-butene or 2-butene with biphenyl at a mol ratio of butene to biphenyl of from about 0.5 to about 0.9 and at a temperature of about 250° F. to about 475° F. in the presence of an aluminum chloride catalyst, distilling the reaction product under vacuum to remove unreacted biphenyl and distilling off the product mixture at a temperature between about 370° F. and about 440° F. at 30 mm Hg. pressure or the equivalent thereof.

It is known in the art that alkylbiphenyl compounds are useful asdielectric materials. For Example, U.S. Pat. No. 2,172,391, whichdiscloses the alkylation of diphenyl, suggests that ethylated diphenylmay be so used. This reference also points out, however, that alkylationof diphenyl with hydrocarbon of molecular weight above ethylene orpropylene gives more viscous products which form waxlike crystals onstanding. U.S. Pat. No. 2,837,724 discloses the preparation of t-butyldiphenyl and other tertiary alkyl diphenyls for use as a dielectricliquid for transformers. However, 4-t-butyl diphenyl is a solid at roomtemperature (M.P. 50°-51.5° C.) and its use as a dielectric liquid or asa carbonless paper solvent is impractical as it would be limited to useat elevated temperatures. This problem appears to be recognized in thedisclosure of U.S. Pat. No. 4,119,555 relating to use as a dielectricliquid in transformers of a mixture of 30 to 80% by weight of apolychlorobenzene (tri- and tetra-chlorobenzenes) with mono- orpolyalkylbiphenyls or terphenyls. The disclosure points out that for useat low temperatures the dielectric must remain liquid with sufficientfluidity and not give rise to deposition of crystals which are apt toblock or clog pipelines and pumps which circulate the transformer fluidin certain types of apparatus. The disclosure then states that dependingon the physical state at low temperature, the alkyldiphenyls to be usedwith the polychlorobenzenes can be employed in the pure state or asmixtures of isomers and/or of products with different degrees ofalkylation obtained in the course of their preparation. Among a largenumber of alkylbiphenyls to be used with the polychlorobenzenes are thevarious butyl isomers including 3-sec-butyl biphenyl,4-sec-butylbiphenyl, and 4,4'-di-sec-butyl biphenyl, but the thrust ofthe disclosure is the need to use a mixture of the polychlorobenzenesand alkylated bi- or terphenyl. An earlier issued patent, U.S. Pat. No.4,054,937, also discloses the use as a capacitor fluid a mixture ofmono- and di-alkylated biphenyl where the alkyl group is C₂ to C₄ andwhere the fluid comprises 80 to 99% by weight of the monoalkylatedbiphenyl and 1 to about 20% of the dialkylated biphenyl. The preferredspecies are normal alkyl and isopropyl. Alkyl groups above butyl aresaid to have higher pour points and may not be acceptable.

The alkylation of biphenyl with butene is also known in the art to givemixtures of mono- and poly-butyldiphenyls. Zavgorodnil et al(Proceedings of the Academy of Science of the U.S.S.R. pages 9-11, 1958)discusses the alkylation at 50°-100° C. (120°-210° F.) of diphenyl with2-butene in a carbon tetrachloride solvent system using a BF₃.H₃ PO₄catalyst at diphenyl to butene to catalyst ratios of 14:1:0.2-0.3. Attemperatures of 70° C. (158° F.) and higher, the authors indicate thatthe process is accompanied by isomerization of the 2-butene toisobutylene which leads to the formation of a mixture ofp-sec-butylbiphenyl and p-tertbutylbiphenyl. Since, as pointed outabove, the t-butylbiphenyl isomers are solids at room temperature theyare not operable as dielectric oils and their presence in such oilsleads to crystallization at reduced temperatures, thereby destroying theutility of the oil.

It is also known in the art that alkylated biphenyls are useful as a dyesolvent for carbonless paper (see, for example U.S. Pat. No. 4,085,949).U.S. Pat. No. 3,627,581 discloses isopropylbiphenyl and U.S. Pat. No.3,732,141 shows mono-isopropylbiphenyl for this purpose. A mixture ofphenylnaphthyl methanes and C₁ to C₆ alkyl biphenyls is disclosed as adye solvent in U.S. Pat. No. 3,846,331.

It has now been found that a particular mixture of a specific butylateddiphenyl can readily be obtained without the contaminating t-butylisomer and that the mixture has properties making it of particular valueas a dielectric liquid and as a carbonless paper solvent. Such materialis a water-white liquid with a pleasant odor consisting essentially ofabout 82% to 88% (preferably 85%) by weight of mono-sec-butylbiphenyland about 12% to about 18% (preferably 15%) by weight of di-sec-butylbiphenyl. This mixture is readily obtained by alkylation of diphenylwith a highly pure 1-butene or 2-butene or their admixture at a moleratio of butene to biphenyl of from about 0.5 to about 0.9 (i.e. abiphenyl to butene ratio of 2:1 to 1.1:1) at a temperature of at leastabout 250° F. up to about 475° F. in the presence of an aluminumchloride catalyst, and vacuum distilling off the alkylation product at atemperature between about 370° F. and about 440° F. at 30 mm Hg ofpressure. It is unexpected in view of the Zavgorodnil et al articlediscussed above that no t-butylbiphenyl isomer is formed at therelatively high temperatures used in the process of the invention. Whileit is not known why the t-butylbiphenyl isomer is not formed it may bedue to the use of the AlCl₃ catalyst system employed rather than theBF₃.H₃ PO₄ --solvent system of the reference. It is necessary to use atemperature above the 158° F. temperature of the reference in order toachieve a practical and commercially efficient process. Operations attemperatures below about 250° F. would require large scale and expensiveheat exchangers to remove the heat of reaction. By operating at thehigher temperature, however, under applicant's conditions which avoidformation of the t-butyl isomer, a practical commercial process isachieved.

As indicated either 1-butene or 2-butene or their admixture in anyproportion may be used as the olefin for alkylation since they both givethe same product. The butene used, however, must be of high puritybecause other olefins, even other C₄ -olefins, drastically alter theproperties of the alkylate product. Accordingly, the olefin used musthave a purity of at least about 98% of 1- and/or 2-butene.

The catalyst used, as indicated is aluminum chloride. However, it ispreferred to use this catalyst as a complex made from AlCl₃, toluene,and methyl chloride by adding the AlCl₃ (500 parts by weight) to the drytoluene (100 gallons) and then adding the methyl chloride (9 gallons)with agitation. The catalyst complex is a clear, yellow, low viscosityliquid which must be protected from moisture before use. The amount ofcatalyst used is not critical, but the catalyst complex is preferablyused at 0.5 to about 1%, most preferably at a level of 45 gallons ofcomplex per 2500 gallons of biphenyl which corresponds to 0.8 wt. % ofsolid AlCl₃ based on biphenyl. The complex composition is approximately25-30 wt % AlCl₃, 50-60% toluene and 5-10 HCl, the latter derived fromthe added CH₃ Cl.

The butene to biphenyl ratio of between about 0.5 and 0.9 is anotherimportant parameter in order to obtain the desired product. In order toobtain a product with the preferred amount of 15% di-sec-butyl biphenyland with a minimum of tri-sec-butyl product, the ratio should be atabout 0.75. A butene to biphenyl mol ratio of 0.5 can be used to obtainthe desired product but less total product will result per batch. A 0.9mol ratio can also be used but in such case, less of the sec butylbiphenyl can be used in the final product. Commerical practice dictatesthat a mol ratio of 0.75 is about optimum. FIG. 1 illustrates therelationship between mole ratio of reactants and the amounts of thevarious secbutylbiphenyl isomers obtained. It is of interest to notethat at the mole ratio used in the process, the amount oftri-sec-butylbipheny isomer is very low and no tetraisomer is present atall.

The rate of addition of the butene to the biphenyl is not critical, butthe presence of large amounts of unreacted butene in the reaction massshould be avoided in order to prevent the formation of butene polymers.

In carrying out the alkylation the preferred procedure is to pump thecatalyst complex into the molten biphenyl with agitation at about 160°F. The butene or butenes are then added at a rate which allows a maximumtemperature of about 250° F. to be held in the reactor. The mono- anddi-sec-butyl biphenyl isomers, once formed, are very stable to furtherheating under conditions which might be expected to produce undesirableby-products. Alkylation in plant equipment is usually completed over aperiod of from about 3 to about 6 hours.

Upon completion of the addition of the butene, the agitation is stoppedand the entire reactor contents (catalyst plus hydrocarbon) are pumpedto a hydrolyzer where they are contacted with 20 volume % of 20° Be.NaOHsolution at 275°-300° F. for at least 1 hour, preferably 3 hours,followed by a water-wash until neutral. The alkylate is now ready forvacuum distillation.

The principal components of the alkylate at this point are unreactedbiphenyl (b.p. 493° F.), mono sec-butyl biphenyl (b.p. 576°-598° F.), disec-butyl biphenyl (b.p. 598°-691° F.), and higher boiling tri-alkylatedbiphenyls (bottoms).

Following removal of unreacted biphenyl at 296°-340° F. the desiredproduct, containing from about 82% to about 88% mono and from about 14%to about 18% di sec-butyl biphenyl, is obtained from a vacuumdistillation, typically at 30 mm Hg. by taking cuts, preferably fromcuts 2 through 16, (b.p. 370°-440° F.) using a 40 plate Heli-Grid columnor its equivalent at 20:1 reflux ratio as shown in FIG. 2 where theordinate temperature values have been converted to the correspondingvalues at 760 mm Hg. In general, cuts over a range from about 370° toabout 440° F. at 30 mm Hg are useful. It will be understood that, asknown in the art, equivalent pressure--temperature relationships may beused for the distillation. The product is a water-white, liquid with thephysical properties as listed in Table I. The product is essentiallyfree of odor, but any odor that can be detected is pleasant. This lowodor characteristic is a particularly desirable property when theproduct is used as a dye solvent for carbonless paper products and makesthe liquid product of the invention superior to a mixture of 85%monoisopropylbiphenyl and 15% diisopropyldiphenyl which has been usedheretofore for such purpose.

An unexpected and highly desirable property of the liquid product of theinvention is its viscosity, which is an important parameter forelectrical oils and for dye solvents for carbonless paper products. Thelower molecular weight homologue; i.e. the isopropyl biphenyl, has asuitable viscosity for these use applications, but any significantincrease in viscosity would be detrimental. Because, the products ofthis invention are higher homologes and have a higher molecular weightthey would be expected to have a significantly higher viscosity and thisis, in fact, the case with the t-butyl compounds which, as pointed outabove are viscous liquids or solids. Surprisingly, however, theviscosity of the liquid products of this invention are not significantlyabove that for the lower homologue and this is shown in the followingTable II:

                  TABLE I                                                         ______________________________________                                        TYPICAL PRODUCT PROPERTIES                                                                    Properties                                                    ______________________________________                                        Composition                                                                   Total Aromatics, Wt. %                                                                          99.0                                                        Mono sec-Butyl Biphenyls,                                                                       81-87                                                       Wt. %                                                                         Di sec-Butyl Biphenyls,                                                                         12-18                                                       Wt. %                                                                         Total Sulfur, PPM nil                                                         Total Halogens, PPM                                                                             nil                                                         Volatility                                                                    Engler Distillation, °F.                                                                 --                                                          (ASTM D-86)                                                                   IBP               578                                                         End Point         610                                                         Flash Point, COC, °F.                                                                    315                                                         General                                                                       Gravity           13.9                                                        Specific Gravity, 60/60 ° F.                                                             0.9763                                                      Color, Saybolt    +22                                                         Acidity, TAN, mg./g. KOH                                                                        nil                                                         Odor              Pleasant (essentially odorless)                                               Aromatic                                                    Viscosity, SUS @ 100° F.                                                                 49.1                                                        RI, n.sub.d.sup.20                                                                              1.573                                                       Pour Point, °F.                                                                          <-50                                                        KB                64                                                          ______________________________________                                    

                  TABLE II                                                        ______________________________________                                        Saybolt Viscosity Values (SUS C 100° F.)                               Isopropylbiphenyls                                                                             Sec.-Butylbiphenyls                                          85/15 Mono/Di    85/15 Mono/Di                                                ______________________________________                                        43.0 ≠ 1.5 49.1 ≠ 1.5                                             ______________________________________                                    

EXAMPLE

Following the details outlined above, 20,000 pounds (2,500 gallons) ofbiphenyl was alkylated at 250° F. with 5,190 lbs (1,050 gallons) of1-butene (mol ratio of butene:biphenyl=0.75) using 45 gallons of anAlCl₃.Toluene.CH₃ Cl complex catalyst which corresponds to 0.8 wt % ofsolid AlCl₃ based on biphenyl. After accumulating cuts distilling at370° F.-440° F., (at 30 mm Hg) the product contained 85% by weight ofthe mono-sec-butylbiphenyl and 15% of di-sec-butylbiphenyl as determinedby gas chromotography. The colorless product had a Saybolt viscosity(SUS C 100° F.) of 49.1, was essentially free of odor and when evaluatedas a carbonless paper solvent for the dye was found to be quitesatisfactory for commerical use. The product had the electricalproperties shown in Table III and was also commercially acceptable asthe dielectric oil in an electrical capacitor wherein the paper spacerwas impregnated with the product.

                  TABLE III                                                       ______________________________________                                        Electrical Properties of 85/15                                                Mono/Di Sec-Butylbiphenyl                                                     ______________________________________                                        Dielectric Constant                                                                              2.5 (ASTM D-924)                                           @ 100° C.                                                              Power Factor       0.45% (ASTM D-924)                                         @ 100° C.                                                              Dielectric Strength                                                                             66.0 KV (ASTM D-877)                                        ______________________________________                                    

The liquid composition of the invention is also advantageous in that ithas very favorable biological properties; e.g. ready biodegradabilityand low toxicity as shown by the tests summarized in Table IV.

TABLE IV BIOLOGICAL TEST DATA OF 85/15 MONO/DI SEC BUTYLBIPHENYLBiodegradation:

Test Compound biodegraded by tenth day;

Skin irritation (rabbits): The test material is not an irritant (bydefinition). Two animals had severe skin reactions, but at 14 days, allsites were normal or nearly normal.

Acute dermal toxicity (rabbits): The test substance is considered to bea relatively mild skin irritant.

Eye irritation (rabbits): Based on the results of unwashed eyes, theirritation potential of the test material is undeterminate (2 out of 9had eye redness, etc.).

Based on the results of washed eyes, no animals had any redness, etc.

Oral toxicity (rats): LD/50 is greater than 5.0 g/kg. The test materialis not considered to be toxic.

Inhalation (rats): No mortality. Within two hours of exposure rats wereeating and drinking; all animals gained weight. No abnormalities ofinternal organs.

Ames test: Material did not demonstrate genetic activity in any of theassays and was considered non-mutagenic under the test conditions.

The invention claimed is:
 1. A water-white, essentially odorless liquidcomposition useful as a dielectric oil and as a dye solvent, consistingessentially of about 82% to about 88% by weight ofmono-sec-butylbiphenyl and about 12% to about 18% ofdi-secbutylbiphenyl.
 2. The composition of claim 1 consistingessentially of about 85% of mono-sec-butyl biphenyl and about 15% ofdi-sec-butyl biphenyl.
 3. A process for preparing a water-white,essentially odorless liquid product useful as a dielectric oil and as adye solvent, consisting essentially of about 82% to about 88% by weightof mono-sec-butylbiphenyl and about 12% to about 18% ofdi-sec-butylbiphenyl which comprises reacting highly pure 1-butene or2-butene with biphenyl at a mol ratio of butene to biphenyl of fromabout 0.5 to about 0.9 and at a temperature between about 250° and about475° F. in the presence of an aluminum chloride catalyst, distilling thereaction product under vacuum to remove unreacted biphenyl andthereafter distilling off the liquid product mixture at a temperaturebetween about 370° F. and about 440° F. at 300 mm Hg. pressure or theequivalent thereof.
 4. The process of claim 3 wherein the ratio ofbutene to biphenyl is about 0.75 and the liquid product is distilledover a temperature range of from about 370° F. to about 437° F. at 30 mmHg.
 5. The process of claim 4 wherein the catalyst used is a complex ofAlCl₃ with toluene and methyl chloride.
 6. A process for preparing awater-white, essentially odorless liquid product useful as a dielectricoil and as a dye solvent, consisting essentially of about 85% by weightof mono-sec-butylbiphenyl and about 15% of de-secbutylbiphenyl preparedwhich comprises reacting highly pure 1-butene or 2-butene, or theiradmixture with biphenyl at a mol ratio of butene to biphenyl of fromabout 0.75 and at a temperature of about 250° F. in the presence of analuminum chloride complex catalyst, distilling the reaction productunder vacuum at a temperature between about 296° and 340° F. to removeunreacted biphenyl and thereafter distilling off the liquid productmixture at a temperature between about 370° and about 440° F. at about30 mm Hg pressure.